Bone cutting guides for use in the implantation of prosthetic joint components

ABSTRACT

Improved bone cutting guides enable a surgeon to better gauge required resection characteristics. In one embodiment at least a portion of the guide is transparent, thereby enabling the user to optimize cut estimates and to visualize the resection as it is being performed. In another embodiment, at least a portion of the outer surface of the body is shaped to interact with another bone or prosthetic element associated with a joint, thereby enabling the device to function both as a trial and as a cutting guide. In this embodiment as well the guide may be at least partially transparent to improve visualization. Although primarily intended for use in femorat-side knee arthroplasty, the invention is applicable to any procedure which might benefit from improved bone-cutting accuracy.

FIELD OF THE INVENTION

This invention concerns arthroplasty, and, more particularly, resides inimproved cutting guides having features to better assist a surgeon inpreparing a bone, for example, to receive an implant.

BACKGROUND OF THE INVENTION

Whether for primary or revision arthroplasty, cutting guides aretypically employed to ensure that the bone saw performs resectionscorresponding to mating surfaces of the prosthetic component. Forexample, in a femoral knee replacement, cutting guides or blocks aretemporarily secured to the distal end of the femoral shaft, and includeslots into which the blade of an oscillating saw is inserted to shapethe end of the bone in accordance with corresponding surfaces of theprosthetic element.

In the case of a revision, the procedure is usually more elaborate dueto deterioration of the previously prepared surfaces resulting fromdecomposition of the bone/prosthesis interface, necrosis, and otherfactors. Cutting blocks are also typically used in revision procedures,though bone deficiency often renders stabilization of the blockimpossible. In addition, if the cutting block includes a stem, thepositioning of the stemmed implant can alter the fit of the finalprothesis relative to the bone. More recently introduced techniquesattempt to base the cuts on an intramedullary guide to which additionalcutting blocks are mounted. Though such approaches improve bone cuttingaccuracy; there remains an unacceptable margin of error, the correctionof which in some cases requiring a freehand shaping of the bone.

SUMMARY OF THE INVENTION

The present invention accordingly provides improved cutting guides whichenable one performing a resection to better predict and execute requiredcue characteristics. Broadly, at least a portion of the body comprisingthe cutting guide is transparent, thereby enabling the practitioner tobetter estimate cut depth and/or visualize the resection as it is beingperformed. Preferably one or more slots are used to guide a cutting saw,with the volume of the body surrounding the slots being transparent.

In one embodiment, at least a portion of the outer surface of the bodyis further shaped to interact with another bone or prosthetic element aspart of a joint, thereby enabling the device to function both as a trialand as a cutting guide. For example, if adapted for use in femoral kneearthroplasty, the outer shape of the body may include condylarprotrusions which cooperate with corresponding tibial surfaces orprosthetic inserts. In this combination trial/cutting-guide embodimentthe device may likewise advantageously be at least partially transparentto assist in estimating cut orientation or depth, and to visualize aparticular resection in progress. Although primarily intended for use inconjunction with preparing a bone surface to receive a prostheticcomponent, the invention is applicable to any bone-cutting procedurewhich might benefit from improved accuracy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an oblique drawing of the distal end of a femur, showing someof the resections typically used in conjunction with prostheticimplantation;

FIG. 2 is an oblique drawing of a cutting guide adapted for primaryfemoral knee arthroplasty which, according to the invention, isconstructed of transparent material;

FIG. 3 is an oblique drawing of an existing prosthetic component adaptedfor mounting on the distal end of the femoral shaft including anintercondylar box structure;

FIG. 4 is an improved cutting guide according to the invention, whichincludes outer surfaces appropriate to trial testing combined withcutting guides to facilitate efficient resection;

FIG. 5 illustrates from an oblique perspective an alternative embodimentof the invention which facilitates box cuts if not already present;

FIG. 6 is a top view of yet a further alternative embodiment of theinvention involving the use of a box-cutting implement which may beremoved from an implanted stem onto which a combination trial andcutting guide may subsequently be installed;

FIG. 7 is a top view drawing of the combination trial/cutting guidereferenced above with regard to FIG. 6, now in position on the implantedstem; and

FIG. 8 is yet a further alternative embodiment of the inventionincluding a stem configuration which facilitates at least partial boxcut formation along with guides for other resections in a femoral kneeapplication.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1 there is depicted a distal end portion 104 of a femur 102,which terminates in two bulbous protrusions 105 termed the medial andlateral condyles, which mate and engage with corresponding surfaces inthe proximal end of the tibia. As a result of disease or injury, thesemating surfaces, ordinarily smooth and cushioned by an interveningcartilage layer, disintegrate and/or become misshapen, resulting inrestricted movement and pain.

To ameliorate these conditions, the orthopedic surgeon removes theunhealthy bone stock and replaces it with one or more metalliccomponents which adhere to appropriately prepared bone surfaces andapproximate the outer, cortical layer of a healthy bone. To prepare theexisting damaged or diseased bone to accept the implant components,various resections are made in a predetermined manner in correspondencewith the inner surfaces of the implant. Using the femoral example ofFIG. 1, a saw guide is used to form resected surfaces resulting from ananterior chamfer cut 106, distal femoral articular surface cut 108,posterior chamfer cut 110, posterior-articular surface cut 104 112,and/or anterior articular surface cut, which is typically performedprior to the articular chamfer cut. Although these cuts representresections made in conjunction with a standard implant technique, more,fewer or different surfaces may be required, depending upon the level ofdeterioration or other circumstances.

Depending upon the saw guide used, either the cuts associated with onlyone of the condyles may be resected, or, alternatively, a guide having adual set of slots may be utilized to trim both condyles simultaneously.A singular type fixture is shown, for example, in U.S. Pat. No.5,122,144, whereas guides having double sets of slots are shown in U.S.Pat. Nos. 5,129,909 and 5,364,401. Numerous other examples are evidentin the prior art, some of which are in commercial usage. The cutsassociated with revision arthroplasty of the femoral component in a kneereplacement are similar to those depicted in FIG. 1, though nowadditional bone stock must be removed, and additional cuts closer to thecentral axis of the bone are typically made to accommodate a one-piecereplacement unit having a intercondylar strengthening structure andposts extending therefrom for intramedullary implantation. Such arevision knee prosthesis is shown, for example, in U.S. Pat. No.4,936,847.

Whether for primary or revision arthroplasty, the saw guides involvedare without exception now constructed of metal, and they are thereforevisually opaque. This results in a substantial piece of hardware whichmay be washed, sterilized and used repeatedly in numerous procedures,but, being opaque, the orthopedic surgeon is simply unable to see whathe or she is doing while making the various bony cuts. As a result, itis often standard practice to make one or more cuts with the guide inplace, then move the guide aside in order to view the interface, toensure that sufficient bone has been removed to facilitate the mostideal cement interface between the resected bone and implant component.This trial-and-error process not only consumes valuable time during theoperation, but may lead to the removal of more bone stock than necessaryto achieve fixation.

During revision arthroplasty, such trial-and-error is that much morecomplicated and arduous, owing to the increased number of resectedsurfaces involved, and the need to ensure that these surfaces and themedullary stem are all properly aligned during the testing of trialimplants and the attachment of the final prosthetic device. In the eventof a misalignment, the surgeon may choose to use a final implant havinga smaller than optimal diameter stem, for example, to take up the slackupon discovering a slight misalignment with respect to the stem and theresected surfaces. This, in turn, may lead to an undesirable "play"between the stem of the prosthesis and the reamed medullary canal,and/or the need for medullary cementation which might otherwise beunnecessary.

According to this invention, then, improved cutting guides are providedto better assist the surgeon in performing accurate resections in anefficient manner. For example, guides adapted for use with primaryarthroplasty have transparent features according to this invention, atleast in the vicinity of the saw-receiving slots, thus enabling thesurgeon to visualize the way in which the existing bone makes contactwith the inner surfaces of the guide, and therefore facilitates a muchmore exacting initial set of cuts, in most cases, ideally eliminatingtrial-and-error entirely. In the case of revision work, the cuttingguide itself contains condylar and other outer surfaces enabling it tofunction both as a cutting guide and as a trial. Accordingly, once aninitial trial procedure is carried out, the various resections may beperformed, with a greater likelihood that they will be properly located,thereby increasing accuracy. Although a revision guide according to thisinvention need not be transparent, the combination of a combinedtrial/cutting guide constructed of a transparent material is preferredto realize the advantages set forth above.

FIG. 2 illustrates one version of a cutting block constructed inaccordance with the invention, in this case a guide for use in makinginitial articular surface and chamfer cuts. Positioning of the blockassumes the surgeon has first made a distal femoral articular surfacecut against which the backside (not shown) of block 204 is seated whilemaking these further resections, the chamfer cuts being angular withrespect thereto. This block 204 may be held against the bone through anyattachment or stabilization means, including screws, pins, braces orother fixtures so long as the guide is appropriately secured.Importantly, and unlike all existing guides of this type, at least theright and left portions 208 and 210 are composed of a transparentmaterial, and, preferably, the entire unit is clear and constructed ofacrylic, polycarbonate or any other plastic or material substantialenough to withstand the oscillations of a bone saw or other cuttingtool, yet sufficiently transparent to enable a surgeon to visualize thesurfaces to be resected in conjunction with a particular procedure.Preferably, this unit and others to be described of a cast plasticmaterial such as acrylic or Lucite, having polished surfaces, wherenecessary, improve visualization.

In the case of primary arthroplasty, a cutting guide according to theinvention need not assume the characteristics of that shown in FIG. 2,but may assume any suitable form and may be used for any bone-formingpurpose, whether or not resulting from trauma. For example, the unit mayresemble that shown in FIG. 20 of U.S. Pat. No. 5,234,433, which furtherincludes a guide slot to accommodate not only the cuts just described,but, in addition, the distal femoral articular surface cut creatingsurface 108 in FIG. 1. For that matter, the broad principles of thisinvention are applicable to any type of cutting fixture, whether slottedor otherwise, adapted for use for prosthetic resection which mightbenefit from having any transparent portions or panels to assist thesurgeon in better visualizing the bone preparation process. Thisembodiment and those discussed below may also be adapted for use withcutting tools other than saw blades, including osteotomes, router bits,etc.

Reference will now be made to FIGS. 3-8, which represent embodiments ofthe invention more suitable revision arthroplasty. Before discussing theimproved devices and methods made possible through the invention,however, existing approaches will first be discussed with particularregard to femoral knee surgery. In preparing the femur for a revisionimplant, the procedure may typically first include a drilling andreaming of the medullary canal to accept a sleeve and rod which extendsoutward and past the distal tip of the femoral shaft, and onto whichvarious components are temporarily secured and stabilized to facilitatethe various resections. For example, to perform the distal revisionresection, an outrigger may be secured to the protruding stem and ontothis placed a revision distal femoral cutting block, typically furthersecured with pins, screws, or other means engaged with the anteriorcortex. Such a distal cutting guide typically includes various slots oneither side to accommodate the lateral and medial resections atdifferent depths according to the level of bone loss on either side.

Having prepared the distal surfaces, this first cutting block is removedand an anterior/posterior cutting block is installed onto the stem alongwith spacers in the event of different depths of the lateral and medialdistal resections. With the anterior/posterior cutting block secured inplace, again with pins or screws, the anterior and posterolaterallateral cuts are made. Although the anterior cut is typically easilyvisualized as this region of the femoral shaft is fully exposed duringthe procedure, as with the lateral resection(s), the posterolateral andposteromedial cuts are almost entirely hidden from view. Once theanterior and posterior resections are carried out, the cutting guideassociated therewith is typically removed, and onto the medullary stemthere is placed yet another guide used to perform notch and chamferresections.

FIG. 3 illustrates a typical prior-art revision implant, andadditionally shows the orientation of the notch or "box" cuts toaccommodate the intercondylar structure 302, which includes a transversesurface 304 and side surfaces 306 and 308 (not visible). The structureis box-shaped so that flat saw blades may be used to resect the bone andprovide a more intimate and stable interface. As discussed above, thisbox-like structure 302 provides strengthening between the two condylarhalves, and allows room for superior post protrusion inposterior-stabilized designs. The structure 302 also supports the stem310, which is threadingly or compress-fit thereinto. A notch and chamfercutting guide is typically used for the chamfer cuts and the cutsassociated with the sides 306 and 308 of the intercondylar box, althoughthe stem is typically removed to perform proximal anterior chamferresections. The stem of the fixture must also be removed in order tomake the transverse cut corresponding to the surface 304.

Once all such guides or their equivalents have been used for the variouscuts, the orthopedic surgeon typically must further progress through atrial reduction procedure which has matching inner surfaces, but varyingthicknesses between the inner surfaces and the outer joint surfaces,which are each tested, in turn, to ensure a correct joint line andfemur-to-tibia orientation. Trial polyethylene inserts are also selectedto provide maximum range of motion and stability, at which point thefemoral component may be implanted, in some cases utilizing spacers toaccommodate the depth of cut determined as a function of bone loss. Suchspacers typically clip into place, as shown in FIGS. 1 through 4 of U.S.Pat. No. 4,936,847.

It should be evident from the steps just described, that numerous guidesmust be resorted to as part of a lengthy trial-and-error procedurewhich, even when carried out in a comprehensive manner, may lead toslight or even gross misalignments upon fixation of the final implantcomponents. The present invention solves many of these problems byproviding cutting guides having transparent sections enabling thesurgeon to visualize the underlying bone stock before, during and aftereach resection. In the case of the revision situation, or as part of aprimary procedure wherein cutting blocks have been used, the inventionfurther eliminates the need for a protracted trial reduction procedureby providing a cutting guide in the shape of the final implantcomponent, thereby ensuring that once the guide is removed, the finalimplant component will inherently match the executed resections, therebysaving considerable time while improving accuracy.

One version of a cutting block according to the invention for femoralknee revision work is depicted in FIG. 4. In this particular embodiment,a combination trial and cutting guide is provided under the assumptionthat box cuts have previously been made to accept the intercondylarstructure 404. Broadly, in this case, the device includes one or moreinner surfaces which are configured for correspondence with theresections carried out during the primary procedure, but, according tothe invention, the device also includes outer surfaces which approximatethe trial prosthesis or final implant shape, including outer condylesurface protrusions, only one side of which is partially visible as 404in the figure. The device also includes a femoral stem 450, which may bedetachable, as well as means for temporarily securing the device to thedistal end of the femoral shaft, such as thumb screws 408, which areadapted for engagement with anterior cortical regions, or, as analternative, stabilization pin holes 410 associated with securing thedevice laterally or posteriorly. Any type of temporary securement meansmay be substituted for this optional feature, including tighteningbands; outriggers, braces, or any combination of manually operatedfasteners or pin-receiving holes or guides, so long as the unit is heldin position throughout the procedure.

To simultaneously function as a cutting guide, the device of FIG. 4 alsoincludes one or more slots such as 412 into which a conventional,oscillating saw blade may be inserted to perform a required resection.In the embodiment depicted in FIG. 4, the device is preferably somewhatwider than the final implant, by an amount depicted as "W" shown in thefigure, to provide additional material beyond the slotted areas forgreater structural stability. Inner surfaces of the device areproportioned, where necessary, by an amount "d" representative of thethickness of the cutting tool used to ensure that, once the combinationtrial/cutting guide is removed, the final implant mates accuratelyagainst the surfaces resected. Preferably the device accommodatessufficient slots and/or surfaces to perform all of the cuts necessarybefore the installation of a conventional revision prosthetic component,though alternative embodiments may include more or fewer such slots toaccommodate a particular or specialized procedure. Depending upon theparticular resection to be performed, multiple slots may also beprovided to shape a particular surface, the depth of the slot finallyrelied upon being a function of bone deterioration in a particularregion. For example, FIG. 4 shows a set of two slots 416 for the distalcondylar cuts and two slots 418 associated with trimming the bottom ofthe box resections. Preferably, such multiple slots, which may be two ormore, are separated by an amount related to existing spacers, forexample, 4 mm.

It should already be apparent that the invention is suitable to femoralknee revision arthroplasty whether or not box cuts have been provided aspart of a primary procedure. If provided, the device of FIG. 4 may beused directly; if not, the device of FIGS. 5-8 may alternatively beused. The structure shown in FIG. 5 is quite similar to that depicted inFIG. 4, except the box structure 404 has been replaced with a passageway506. The device still includes outer condylar surfaces, however,enabling the device to be used as both a trial and a cutting guide. Thisfigure also shows an oscillating saw blade being placed in differentslots or against different surfaces to provide the requisite cuts. Forexample, saw blades 514 and 515 inserted through slots 512 or 513, maybe used to form transverse intercondyle cuts, whereas, blades inpositions 520 and 522 may be inserted for the chamfer cuts, and so on.In addition, although slots are not shown, by placing the blade againstthe surfaces 530 (not visible) and 532, cuts corresponding to the sidesof the box structure may be performed. Blades in positions 540 and 542may be used to make the bottom cuts associated with the box. In the caseof position 540, the blade could rest against a surface (not shown)provided on the device, whereas a slot 543 may be provided for a deeperbox bottom cut using blade 542.

FIGS. 6 and 7 illustrate a further alternative embodiment for accuratelyproviding box cuts in the event that such cuts were not performedpreviously. In FIG. 6, there is shown a block 604 removably attached toan implanted intermedullar stem 602. Once in place, a saw blade atposition 608 may be moved along the left surface of the block 604 tomake a side box cut 606, and a blade in position 610 may be moved alonga right surface of the block 604 to make a box cut 612. As analternative to the use of outer surfaces of a cutting block such as 604,a guide with slots may also be removably attached to the stem 602. Tomake the bottom cut of the box, a blade may be moved straight down intothe page, riding against a rearward surface 618.

Now making reference to FIG. 7, a device similar to that depicted inFIG. 5 is shown generally at 702. Instead of providing a passageway 506against which a flat saw may be placed to provide the box cuts, separateslots 705 are provided specifically for this purpose. This particulardevice may include a stem 706, but since the box cuts are not yetavailable, a trial is carried out in conjunction with a specializedtibial spacer 710 not having superior post protrusions should the jointconfiguration be stabilized in this manner. Once the cuts 705 areperformed, the overall device may be removed from the stem 706, and,assuming the stem connection is sufficiently deep in the bone, the cutcorresponding to the bottom of the box may be completed. Then a devicesuch as that shown in FIG. 4 may be inserted, as required, to carry outany necessary subsequent resections.

FIG. 8 shows yet another further alternative embodiment of theinvention. In this particular design, a stem 804 is provided, which isremovably attachable to the bulk of the trial/cutting guide assembly 810at an interface 812. As a compromise between the passageway 506 shown inFIG. 5 and the complete box structure 404 shown in FIG. 4, the stem 804connects to a smaller box-shaped element 820, enabling a saw to beplaced on either side to perform the side box cuts, as shown in phantomat 824 for the one side, or used from above to form the bottom surfaceof the box with a saw shown at position 830. Having carried out at leastthis partial bottom surface cut, the bulk of the element may be removedfrom the stem 804 at interface 812 and the saw in position 830 extendingdownwardly to finish off the bottom box surface cut. With the box cutshaving been performed and with the stem 804 remaining in place, a devicesuch as that shown in FIG. 4, with the stem 450 being removable from thebox 404 at the interface 460, may then be installed and the remainingresections performed.

In use, then, the invention affords a procedure which, in at least onerespect, is essentially opposite to steps now being performed. That is,rather than making the various cuts (including the use of different sawguides), then performing a trial reduction, by using the presentinvention, in essence, a trial reduction is performed first with a trialhaving saw guide slots or surfaces. Once the various cuts have beenmade, the inventive combined trial/saw guide is removed, at which pointthe surgeon realizes precisely which final implant to choose forpermanent affixation. Not only will the surgeon know which finalprosthetic component to select, but he or she will also know whichspacers to use based upon the depth of slot used for the cut, and, sincethe combined trial/saw guide of this invention may be constructed withprior knowledge of the final implant configuration, misalignments of thetype discussed earlier with regard to the implant stem are minimized.Due to the fact that a single guide may be used to perform numerous,accurate cuts, the invention should save considerable time whileincreasing the precision of both primary and revision arthroplasty in awide variety of joint replacement and other orthopaedic situationsincluding the tibial side of a knee replacement.

Having thus described my invention, I claim:
 1. The method of preparingan end of a bone having surfaces requiring resection in order to receivea joint-related implant, comprising the steps of:providing a combinationtrial and cutting guide; installing the combination trial and cuttingguide onto the end of the bone before performing any of the resections;reducing the bone with the guide installed to test the joint; and upon asatisfactory reduction, with the cutting guide installed, performing allof the resections, as required.
 2. The method of claim 1, wherein theend of the bone is a distal femur, and wherein the step of providing acombination trial and cutting guide includes the step of providing sucha guide having outer condylar surfaces configured to co-act in a kneejoint.
 3. The method of claim 2, wherein the combination trial andcutting guide includes bone-modification guides capable of performing adistal cut and a posterior cut.
 4. The method of claim 2, including thestep of providing a combination trial and cutting guide includes one ormore guides capable of performing a box cut of the type associated withcruciate-sacrifice knee-replacement surgery.
 5. In revision kneearthroplasty, wherein a final implant having outer condylar surfaces andan intercondylar box structure associated with a cruciate-sacrificingprocedure is to be installed onto the distal end of a femur, the methodof preparing the femur to receive the final implant, comprising thesteps of:performing a series of box cuts into the end of the femursufficient to receive the box structure, including the stepsof:installing an intermedullary guide post, installing onto the guidepost, a rectangular structure having surfaces which correspond to thebox cuts, and performing the box cuts using the surfaces of therectangular structure as references, providing a trial implant havingouter condylar surfaces and a box structure which correspond to those ofthe final implant, the trial implant further including a plurality ofbone-modification guides sufficient to perform all anterior, posterior,angled, and axial resections necessary to receive the finalimplant;installing and securing the trial implant to the distal end ofthe femur; performing a trial reduction with the trial implant in place;and in the event of a successful trial reduction, performing allrequired resections using the bone-modification guides, removing thetrial implant, and installing the final implant.
 6. A trial implant forfemoral revision knee arthroplasty including a cutting guide forperforming box cuts associated with a cruciate-sacrificing procedure,the trial comprising:a solid body having an outer condylar surface and aplurality of inner surfaces which correspond to resected surfaces on thedistal end of a femur; and a rectangular aperture formed through acentral region of the body, the aperture having one or more sidesurfaces which may be used as references to perform the box cuts.
 7. Thetrial of claim 6, further including one or more slots into which a sawblade may be inserted to trim one of the resected surfaces.
 8. The trialof claim 6, wherein the spacing between the outer condylar surface andthat of at least one of the inner surfaces is slightly less than thecorresponding thickness of the final implant to account for thethickness of the saw blade.